Braun tube



K. SCHLESINGER April 13, 1937.

BRAUN TUBE Filed Jul 6, 1934 Driven For: W7

Patented Apr. 13, 1937 v UNITED STATES" PATENT OFFICE Germany July 8,1933 50laims. .(oi. 250-2 15) In the application Ser. No. 730,111 filedJune 11th, 1934, there is described a cathode ray tube for televisionpurposes operating under high vac-, uum, in which the electronic ray iscontrolled in its intensity, preferably by space charge control,

and is preliminarily concentrated by the use of suitable electrostaticfields,,or if desired also by the use of intermediate diaphragms, andprojected on to a diaphragm. The aperture of this diaphragm is thenreproduced on the luminous screen of the Braun tube by anelectron-optical system having a constant focal distance. Since thediaphragm aperture acts as a surface of constant form and size but withvarying light intensity, it is possible in this manner to produce imagepoints, the form and size of which is independent of their intensity andin consequence remain unaltered even when a change-over takes place fromlightest white to deepest black. In

this manner the errors in light control are obviated without the use ofgas concentration solely by electrostatic devices which act as lenses.

The present invention relates to a technical form of embodiment of atube of this nature, in which 5 preferably twoelectrbstatic lenses andone condenser are employed.

Fig. 1 shows a section through the tube. A diaphragm aperture l in aplate 2 is employed as the object to be'reproduced, and is reproduced on0 the screen 5 by means of two collecting lenses 3 and 4 disposed onebehind the other. The dia- I phragm aperture I, exactly as in theoptical art, is reproduced in reverse form on the screen, enlarged inaccordance with the ratioof the distance between the refractive planeand the screen 5 on the one hand and the refractive plane and thediaphragm l, on the other hand. It is quite readily possible to impartto the fluorescent point any desired geometric form by giving theaperture l a corresponding shape. The practical dimensions areconveniently selected in such fashion that the reproduction takes placeas far as possible merely with slight enlargement. The distance betweenthe diaphragm l and the lens 4 should accordingly be as large aspossible compared with the distance between 4 and 5. In practice theformer may amount to 140 mm. and the latter to250 mm., so that anenlargement takes place to merely approximately twice the size. The mostextensive reduction possible of the reproduction of the diaphragmaperture on the screen should be sought to be obtained. This might beaccomplished, for example, by shortening the distance between 4 and 5.To reduce still further the distance of the screen would be possible initself, but would be accompanied by the disadvantage of a decreasedsensitivity in the expanse of movement,.so that with the same deflectingpotentials the size would be smaller. It has been found that difficultyexists in producing over such a great length of tube (for example mm.)an electronic ray having the required density and such a small angle ofdivergence that the same at the point of the rear lens 4 still passescleanly through the lens aper- 10 ture. On the other hand nodifliculties are encountered in making adjustment for-a veryconsiderable density of current at the point of the diaphragm I ifthemarginal rays ofthe outgoing bundle are permitted to have a greaterdil5vergence.

It has been found, however, in accordance with the invention, that inthe case of a current density of 1 milliampere per mm. at a diaphragmaperture I of .5 mm. diameter with the condenser'ar- 20 rangements andcathodes described more concisely in the following a cross-section ofthe bundle of less than approximately 10 mm. is difficult to obtain atthe point of the rear lens. If

on the other hand an attempt is made to reduce 25 the cross-section atthat point, this can only be done if at the same time the rays impingingagainst 2 are made parallel, a large part of the energy being withheldin useless fashion from the diaphragm plate 2, this resulting in aconsid- 3O erable loss of light.

One object of the invention accordingly resides in the use of a secondlens, i. e., the front lens 3. This lens 3 is approached .to within ashort distance, i. e., approximately half. the length of 3 the tube,towards the diaphragm I. The same is so adjusted that the same alone isable to project on the screen merely a virtual image, and is so arrangedbetween diaphragm and screen that its actual image of the diaphragm l ispreferably 40 smaller than or at, the most equal to the crosssection ofthe bundle at the screen 5 determined by the opening of 4 and .I. It hasbeen found that it'is possible in ideal f hion, with the assistance oftwo lens devices 0 behind the other,.to project an actual reversed imageof .the lens 1 without interfering coma, with a very high density ofcurrent up to 5 milliamperes per mm. in the diaphragm I, possibly with asomewhat greater enlargement than would 50 take place with a single-lenstube having the lens 4 alone. The decisive advantage consists in thefact that at no point is energy lost by selection. It is possible inthis tube to reduce the disadvantage of excessively large image point,since 55 this kind connected one 45 face of which the oxide is pressedinto a recess l,

and which is heated by a heating filament 8. The reproducing elementsfor the surface of the cathode are the cylinders 9 and I0 and the anodesH and 2. The small perforation grid [2, which is situated with 2 mm.aperture at a very short distance amounting to approximately .2 mm.'

in front of the cathode, which has an emissive surface of approximately1.5 mm., serves the purpose of light control, which operates asso-called dark space control. The combination of a negatively biasedcylinder Ill and an after-connected positive diaphragm 2 produces in theknown manner a plane of refraction.- The size of the cathode image onthe anode 2 is all the smaller, the smaller the ratio between thediameter of the cathode l and the focus of the condenser lens l0 2. Thegreater the focal distance of the latter, however, the greater is thedistance at which the luminous object requires to be disposed from thelocation of the plane of refraction H3. A technical compromise leads todimensions as follows: The distance 9ll amounts to approximately 5 mm.,the cylinder I0 to 10 x 10 mm., the distance i l-2 to approximately 20mm. The scale of reproduction is then reduced approximately as 1:3, sothat it is possible to pass the emission of a 1 mm. spot of oxide, whichamounts to approximately 5 milliamperes, quite cleanly through adiaphragm .3 mm. in size.

The cylinder 9 also forms with the anode II a concentrating system,which at the same time accelerates. By selection of the potential at H,and of the drop (i. e. the distance of the emissive surface from theplane of the opening of the cylinder 9) l3 for example at approximately4 mm., with a diameter of cylinder amounting to 10 mm., it may beaccomplished that the bundle of rays entering the lens l0 possesses anangle of divergence as small as desired. According to the invention, itis possible with the dimensions as stated to obtain parallel rays at theplane ll if the anode II is linked up with the full anode potential of2. The sensitivity of the light control amounts to approximately 7volts; in this case the plate II and the cylinder IB' may be omitted andthe plate 2 may be directly used in combination with the cylinder 9.

Particular care is required in the embodiment of the deflecting systems.There is shown in the drawing a double electrostatic deflection by meansof the pairs of plates l4, l5 and I6, ll. According to a further objectof the invention, the smallest spacing between these pairs of plates ismade,

equal to, or larger, but not appreciably smaller than the aperture ofthe rear lens. The length of the plates in the direction of the rays, inthe case of parallel plates, according to the invention is determined bythe maximum angle of movement, with desired size and spacing of thescreen; i. e. the distance between the plates of each system is sodimensioned that the ray, when scanning the edges of the picture to beproduced is almost striking against the respective edges of therespective deflecting plates; In this way it is 'earthed by means ofleads '23.

possible to obtain the greatest possible sensitivity (mm. deflection pervolt) of the deflecting systems In the case of tilted plates the lengthmay be somewhat greater than that of parallel plates. In the practicalembodiment the spacing of the relatively tilted plates may amount forinlet and outlet to 7 and 15 mm., with a lens aperture of 7 mm. andlength of plate in the direction of the rays amounting to 30 mm. Anessential point is the choice of the distance between the plates M, l5on the onehand and'the'lens 4 and the front plates [6,11 on the otherhand. This distance shall preferably amount to at least twice thesmallest distance which may happen to be bebe avoided in the directionof the field lines (infinitely long plates). An additional correction inform if necessary may be performed by the screens l8, i9, 20 and 2i,which just overlap the edges of the plates, and are taken to earth. Forthe purpose of avoiding wall charges the neck of the tube is metallizedfor example silvered, viz., between the point of the lens 4, where thetubular portion 22 of approximately 15 mm. inner diameter terminates,and approximately the middle of the bulb. This wall coating 24 is Thecomplete structure of the tube is performed with the use of non-magneticmaterial, phosphor bronze and glass, with the assistance of specialgauges, for example, in accordance with application Ser. No.

702,313. The tube operates absolutely correctly only if the same issurrounded according to a further object of the invention, with an outerprotective jacket of sheet iron and in this manner protected against theeffect of the earth field.

All deflecting plates may be passed out singly. In this manner thepolarity of both image coordinates may be reversed. All disadvantages ofthe trapezium formation may also be avoided according to Fig. 2 by theuse of mixed electro magnetic deflection. Fig. 2 represents a sectionthrough the neck of the tube viewed from above. The deflecting plates 23and 24 are connected with the line frequency, and at the same timeconstructed as iron pole shoes. 25 is the line-frequency generator. Onthe outside of the glass wall 25 of the tube there are fitted pieces ofiron The magnetcoil of the deflecting system, as'

shown in Fig. 2, may also be constructed in such fashion that the sameconsists of twohigh arches 29, and the coil of two halves, which arewound about the pole shoes.

The potentials for the single electrodes may conveniently be selected,for example, as follows: Cathode heating 8 4 volts, whereby the metalshoes 6 have zero potential, control potential at A ray passing'vertically out of the Wehnelt cylinder-15 to volts, 1. e., e -7.5volts, reproducing element It approximately 0-200 volts, anode 2approximately 2,000 volts, front lens 3 and rear lens 4 approximately 5+1,000 volts, deflecting potentials 2ek=800 volts,

on an average, therefore, 2400 volts.

The diaphragm I 8 may either be raised to anode potential, l. e.,separately from the pair of deflecting plates l 4, l5 or, connected withthe pair of de- 10 flecting plates, linked up with the tiltingpotential.

I claim:

1. 'A Braun tube for television purposes comprising an evacuatedenvelope enclosing an electron source consisting of an indirectly heatedcathode, a Wehnelt-cylinder surrounding said cathode, a controlelectrode'mounted'within said cylinder in front of said cathode, and aplate shaped apertured anode mounted in front of said cylinder, meansincluding said cathode and said 0 anode for producing a cathode ray,said Wehnelt cylinder and said anode forminga pro-concentrating systemfor causing said cathode ray to pass said apertured anode with anopening angle of at most 7 degrees, a fluorescent screen, anelectrostatical electron-optical system comprising a plurality ofapertured electrodes, mounted between said anode and said screen, anddeflecting means for deflecting the cathode ray in two di- 30 rectionsperpendicular to one another for the purpose of scanning said screen.

2. A Braun tube for television purposes comprising an evacuated envelopeenclosing an electron source consisting of an indirectly heated 35cathode, a Wehnelt-cylinder, surrounding said cathode, a controlelectrode mounted within said cylinder in front of said cathode, and anapertured anode arranged in front of said cylinder, and a plate-shapedapertured anode mounted in front of said cylinder, means including saidcathode and said anode for producing a cathode ray, said Wehneltcylinder and said anode forming a preconcentratingsystem for causingsaid cathode ray to pass said apertured anode with an opening angle ofat most 7 degrees, an apertured diaphragm mounted in front of saidanode, a cylinder interposed between and aligned with said anode andsaid apertured diaphragm. said cylinder being adapted to be suppliedwith a potential 50 which is lower than that of said anode, afluorescent screen, an electrostatical electron-optical systemcomprising a plurality of apertured electrodes, said-system producing onsaid screen a sharpimage of said diaphragm aperture and being. 55mounted between said anode and said screen, and

in front 0! said elecintermediate picture of said diaphragm aperture,and a further electron-optical system mounted between saidflrst systemand said screen, said further system reproducing said intermediatepicture on said screen, each of said systems consisting of two aperturedplates and a third element mounted between said plates and consisting ofan apertured plate furnished at one side with a'.cy-- lindrical abutmentthe diameter of whichisconsiderablygreater than the diameter of theaperture of the plate; and means for connecting each of the said plateswith one another.

4. A Braun tube for television purposes comprising an evacuated envelopeenclosing an electron source, means including said electron source forproducinga cathode ray, a diaphragm having a small aperture mounted infront of said electron source, said diaphragm being adapted to besupplied with a positive potential, a fluorescent screen, deflectingmeans for deflecting the cathode ray in two directions perpendicular toone another for the purpose of scanning the screen, one electron-opticalsystem mounted between said electron source and said screen andproducing an intermediate picture of said diaphragm aperture, and afurther electron-optical system mounted between said first system andsaid screen, said further system reproducing said intermediate pictureon ,said screen, each of said systems consisting of two apertured'platesand a third element mounted between said plates and consisting of anapertured plate furnished at one side with a cylindrical abutment thediameter of which is considerably greater than the diameter of theaperture of the plate, one metallic cylinder inter posed between saiddiaphragm and said first electron-optical system, a further metalliccylinder interposed between said two electron-optical systems, thediameter of each of said cylinders being considerably greater than thediameter of each of said apertures and means for connecting each of thesaid plates with 'one another.

5. A Braun tube for television purposes comprising an evacuated envelopeenclosing an elec-' tron source, means including said electron sourcefor producing a cathode ray, a diaphragm having a small aperture mountedin front 0! said electron. source, said diaphragm being adapted tobesupplied with a positive potential, a fluorescent screen, deflectingmeans for deflecting the cathode ray in two directions ilendicular toone another for thepurpose of scanning the screen,

one electron-optical system mounted between j said electron source andsaid screen-and producing an intermediate picture of said diaphragmaperture, and a further electron-optical system mounted between saidfirst system and said screen, said further system reproducing saidintermediate picture on said screen, each of said systems consisting oftwo apertured plates and a third element mounted between said plates andconsistingof an apertured plate furnished at one side with a cylindricalabutment the diameter of which is considerably greater than the diameterof the aperture oi the plate: means for connecting each of the saidplates with one another, and furthermeans for connecting the said thirdelements with one another.

